It seems that PowerShell client doesn't provide much details about errors, so glad you could figure out what the issue was for powershellgallery.com. That message probably could mean a lot of things, and is probably unrelated to TLS/SSL.. So the first thing that's jumping out to me is this: WARNING: Unable to resolve package source 'http://proget.domain.org/nuget/ps' There is no https connection, so there'd be no TLS/SSL issues. But assuming you may have changed the url when posting this... here is a registry key you can use to force that setting (it makes that powershell command unnecessary) https://inedo.com/support/kb/1161/tls-v12-configuration-and-connection-errors If you're on HTTPS the other thing to look at would be certificates. Otherwise, you may need to use something like Fiddler to see the actual request/responses that PowerShell client is issuing/reciveing.